运行LLVM优化器会将32位内存访问转换为64位。有办法避免这种情况吗？

Question

我正在生成的一部分llvm-ir代码上运行llvm优化器。运行优化器后，内存访问将从32位地址转换为64位。我想避免这种情况，因为我用来运行软件验证的工具在64位指针方面存在一些问题。

这是原始代码：

target triple = "i386-unknown-linux-gnu"


@Global_0 = local_unnamed_addr global i32 0
@Global_1 = local_unnamed_addr global i32 0
@Global_2 = local_unnamed_addr global i32 0
@Global_3 = local_unnamed_addr global i32 0
@mem = local_unnamed_addr global [128 x i8] zeroinitializer, align 1

define i32 @main() #0  { 

  func_2_entry: 
    %local_0 = alloca i32
    store i32 0, i32* %local_0
    %local_1 = alloca i32
    store i32 0, i32* %local_1
    %local_2 = alloca i32
    store i32 0, i32* %local_2
    br label %box_0

  box_0: 
    %s_0 = load i32, i32* @Global_2, !Stack !{ !"Stack((s_0, W32Int()))" } 
    br label %box_1

  box_1: 
    store i32 %s_0, i32* %local_1, !Stack !{ !"Stack()" } 
    br label %box_2

  box_2: 
    %s_1 = load i32, i32* @Global_2, !Stack !{ !"Stack((s_1, W32Int()))" } 
    br label %box_3

  box_3: 
    %s_2 = add i32 0, 48, !Stack !{ !"Stack((s_2, W32Int()), (s_1, W32Int()))" } 
    br label %box_4

  box_4: 
    %s_3 = add i32 %s_1, %s_2, !Stack !{ !"Stack((s_3, W32Int()))" } 
    br label %box_5

  box_5: 
    store i32 %s_3, i32* @Global_2, !Stack !{ !"Stack()" } 
    br label %box_6

  box_6: 
    %s_4 = load i32, i32* %local_1, !Stack !{ !"Stack((s_4, W32Int()))" } 
    br label %box_7

  box_7: 
    store i32 %s_4, i32* %local_2, !Stack !{ !"Stack()" } 
    br label %loop_8

  loop_8: 
    br label %box_9

  box_9: 
    %s_5 = load i32, i32* %local_2, !Stack !{ !"Stack((s_5, W32Int()))" } 
    br label %box_10

  box_10: 
    %s_6 = load i32, i32* %local_0, !Stack !{ !"Stack((s_6, W32Int()), (s_5, W32Int()))" } 
    br label %box_11

  box_11: 
    %s_7 = add i32 0, 2, !Stack !{ !"Stack((s_7, W32Int()), (s_6, W32Int()), (s_5, W32Int()))" } 
    br label %box_12

  box_12: 
    %s_8 = shl i32 %s_6, %s_7, !Stack !{ !"Stack((s_8, W32Int()), (s_5, W32Int()))" } 
    br label %box_13

  box_13: 
    %s_9 = add i32 %s_5, %s_8, !Stack !{ !"Stack((s_9, W32Int()))" } 
    br label %box_14

  box_14: 
    %s_10 = load i32, i32* %local_0, !Stack !{ !"Stack((s_10, W32Int()), (s_9, W32Int()))" } 
    br label %box_15

  box_15: 
    %temp_0 = getelementptr inbounds [128 x i8], [128 x i8]* @mem, i32 0, i32 %s_9, !Stack !{ !"Stack()" } 
    %temp_1 = bitcast i8* %temp_0 to i32*, !Stack !{ !"Stack()" }   
    store i32 %s_10, i32* %temp_1, !Stack !{ !"Stack()" } 
    br label %box_16

  box_16: 
    %s_11 = load i32, i32* %local_0, !Stack !{ !"Stack((s_11, W32Int()))" } 
    br label %box_17

  box_17: 
    %s_12 = add i32 0, 1, !Stack !{ !"Stack((s_12, W32Int()), (s_11, W32Int()))" } 
    br label %box_18

  box_18: 
    %s_13 = add i32 %s_11, %s_12, !Stack !{ !"Stack((s_13, W32Int()))" } 
    br label %box_19

  box_19: 
    store i32 %s_13, i32* %local_0, !Stack !{ !"Stack()" } 
    br label %box_20

  box_20: 
    %s_14 = add i32 0, 5, !Stack !{ !"Stack((s_14, W32Int()), (s_13, W32Int()))" } 
    br label %box_21

  box_21: 
    %s_15 = icmp ne i32 %s_13, %s_14, !Stack !{ !"Stack()" } 
    %s_16 = zext i1 %s_15 to i32
    br label %cond.branch_22

  cond.branch_22: 
    %temp_2 = icmp ne i32 %s_16, 0, !Stack !{ !"Stack()" } 
    br i1 %temp_2, label %loop_8, label %loop_8.end

  loop_8.end: 
    br label %box_23

  box_23: 
    %s_17 = load i32, i32* %local_2, !Stack !{ !"Stack((s_17, W32Int()))" } 
    br label %box_24

  box_24: 
    %temp_5 = add i32 16, %s_17, !Stack !{ !"Stack((s_18, W32Int()))" } 
    %temp_3 = getelementptr inbounds [128 x i8], [128 x i8]* @mem, i32 0, i32 %temp_5, !Stack !{ !"Stack((s_18, W32Int()))" } 
    %temp_4 = bitcast i8* %temp_3 to i32*, !Stack !{ !"Stack((s_18, W32Int()))" } 
    %s_18 = load i32, i32* %temp_4, !Stack !{ !"Stack((s_18, W32Int()))" } 

    br label %box_25

  box_25: 
    %s_19 = add i32 0, 4, !Stack !{ !"Stack((s_19, W32Int()), (s_18, W32Int()))" } 
    br label %box_26

  box_26: 
    %s_20 = icmp eq i32 %s_18, %s_19, !Stack !{ !"Stack()" } 
    %s_21 = zext i1 %s_20 to i32
    br label %if_27

  if_27: 
    %temp_6 = icmp ne i32 %s_21, 0, !Stack !{ !"Stack()" } 
    br i1 %temp_6, label %box_28, label %box_32

  box_28: 
    %s_22 = load i32, i32* %local_1, !Stack !{ !"Stack((s_22, W32Int()))" } 
    br label %box_29

  box_29: 
    store i32 %s_22, i32* @Global_2, !Stack !{ !"Stack()" } 
    br label %box_30

  box_30: 
    %s_23 = add i32 0, 0, !Stack !{ !"Stack((s_23, W32Int()))" } 
    br label %box_31

  box_31: 
    br label %if_27_cond.end

  box_32: 
    call void (...) @__VERIFIER_error() #2
    br label %if_27_cond.end

  if_27_cond.end: 
    br label %box_33

  box_33: 
    %s_24 = add i32 0, 0, !Stack !{ !"Stack((s_24, W32Int()))" } 
    br label %func_2_exit

  func_2_exit: 
    ret i32 %s_24

} 

declare void @abort(i32 ) 

declare void @__VERIFIER_error(...) #1

attributes #1 = { noreturn "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
attributes #2 = { noreturn }

作为此代码段中有关指针的示例，使用i32：

%temp_0 = getelementptr inbounds [128 x i8], [128 x i8]* @mem, i32 0, i32 %s_9

我跑步：

opt -always-inline -O2 -S output.ll > output-optimized.ll

使用此版本的opt：

$ opt -version
LLVM (http://llvm.org/):
  LLVM version 6.0.1
  Optimized build.
  Default target: x86_64-unknown-linux-gnu
  Host CPU: haswell

最终结果是：

; ModuleID = 'output.ll'
source_filename = "output.ll"
target triple = "i386-unknown-linux-gnu"

@Global_0 = local_unnamed_addr global i32 0
@Global_1 = local_unnamed_addr global i32 0
@Global_2 = local_unnamed_addr global i32 0
@Global_3 = local_unnamed_addr global i32 0
@mem = local_unnamed_addr global [128 x i8] zeroinitializer, align 1

define i32 @main() local_unnamed_addr {
box_28:
  %s_0 = load i32, i32* @Global_2, align 4, !Stack !0
  %0 = sext i32 %s_0 to i64
  %temp_0 = getelementptr inbounds [128 x i8], [128 x i8]* @mem, i64 0, i64 %0, !Stack !1
  %temp_1 = bitcast i8* %temp_0 to i32*, !Stack !1
  store i32 0, i32* %temp_1, align 4, !Stack !1
  %s_9.1 = add i32 %s_0, 4, !Stack !2
  %1 = sext i32 %s_9.1 to i64
  %temp_0.1 = getelementptr inbounds [128 x i8], [128 x i8]* @mem, i64 0, i64 %1, !Stack !1
  %temp_1.1 = bitcast i8* %temp_0.1 to i32*, !Stack !1
  store i32 1, i32* %temp_1.1, align 4, !Stack !1
  %s_9.2 = add i32 %s_0, 8, !Stack !2
  %2 = sext i32 %s_9.2 to i64
  %temp_0.2 = getelementptr inbounds [128 x i8], [128 x i8]* @mem, i64 0, i64 %2, !Stack !1
  %temp_1.2 = bitcast i8* %temp_0.2 to i32*, !Stack !1
  store i32 2, i32* %temp_1.2, align 4, !Stack !1
  %s_9.3 = add i32 %s_0, 12, !Stack !2
  %3 = sext i32 %s_9.3 to i64
  %temp_0.3 = getelementptr inbounds [128 x i8], [128 x i8]* @mem, i64 0, i64 %3, !Stack !1
  %temp_1.3 = bitcast i8* %temp_0.3 to i32*, !Stack !1
  store i32 3, i32* %temp_1.3, align 4, !Stack !1
  %s_9.4 = add i32 %s_0, 16
  %4 = sext i32 %s_9.4 to i64
  %temp_0.4 = getelementptr inbounds [128 x i8], [128 x i8]* @mem, i64 0, i64 %4
  %temp_1.4 = bitcast i8* %temp_0.4 to i32*
  store i32 4, i32* %temp_1.4, align 4, !Stack !1
  store i32 %s_0, i32* @Global_2, align 4, !Stack !1
  ret i32 0
}

!0 = !{!"Stack((s_0, W32Int()))"}
!1 = !{!"Stack()"}
!2 = !{!"Stack((s_9, W32Int()))"}

如您所见，现在我获得了用于mem访问的i64：

 %temp_0 = getelementptr inbounds [128 x i8], [128 x i8]* @mem, i64 0, i64 %0

我需要在输出中得到的是所有使用i32s而不是i64s的 getelementptr 指令。有什么想法吗？

Answer 1

正如@arrowd在问题注释中指出的那样，添加 target datalayout 元数据可以解决此问题：

p[n]:<size>:<abi>:<pref>:<idx>
        This specifies the size of a pointer and its <abi> and <pref>erred 
        alignments for address space n. The fourth parameter <idx> is a size of 
        index that used for address calculation. If not specified, the default index 
        size is equal to the pointer size. All sizes are in bits. The address space, 
        n, is optional, and if not specified, denotes the default address space 0. 
        The value of n must be in the range [1,2^23).

指定指针位大小的位是 p 选项，我添加了该选项 p：32：32 ，保留对齐和索引大小的默认设置。

最后一行是：

 target datalayout = "e-p:32:32-m:e-i64:64-f80:128-n8:16:32:64-S128"

运行opt命令：

opt -always-inline -O2 -S output.ll > output-optimized.ll

产生预期的结果：

; ModuleID = 'output.ll'
source_filename = "output.ll"
target datalayout = "e-p:32:32-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "i386-unknown-linux-gnu"

@Global_0 = local_unnamed_addr global i32 0
@Global_1 = local_unnamed_addr global i32 0
@Global_2 = local_unnamed_addr global i32 0
@Global_3 = local_unnamed_addr global i32 0
@mem = local_unnamed_addr global [128 x i8] zeroinitializer, align 1

define i32 @main() local_unnamed_addr {
box_28:
  %s_0 = load i32, i32* @Global_2, align 4, !Stack !0
  %temp_0 = getelementptr inbounds [128 x i8], [128 x i8]* @mem, i32 0, i32 %s_0, !Stack !1
  %temp_1 = bitcast i8* %temp_0 to i32*, !Stack !1
  store i32 0, i32* %temp_1, align 4, !Stack !1
  %s_9.1 = add i32 %s_0, 4, !Stack !2
  %temp_0.1 = getelementptr inbounds [128 x i8], [128 x i8]* @mem, i32 0, i32 %s_9.1, !Stack !1
  %temp_1.1 = bitcast i8* %temp_0.1 to i32*, !Stack !1
  store i32 1, i32* %temp_1.1, align 4, !Stack !1
  %s_9.2 = add i32 %s_0, 8, !Stack !2
  %temp_0.2 = getelementptr inbounds [128 x i8], [128 x i8]* @mem, i32 0, i32 %s_9.2, !Stack !1
  %temp_1.2 = bitcast i8* %temp_0.2 to i32*, !Stack !1
  store i32 2, i32* %temp_1.2, align 4, !Stack !1
  %s_9.3 = add i32 %s_0, 12, !Stack !2
  %temp_0.3 = getelementptr inbounds [128 x i8], [128 x i8]* @mem, i32 0, i32 %s_9.3, !Stack !1
  %temp_1.3 = bitcast i8* %temp_0.3 to i32*, !Stack !1
  store i32 3, i32* %temp_1.3, align 4, !Stack !1
  %s_9.4 = add i32 %s_0, 16
  %temp_0.4 = getelementptr inbounds [128 x i8], [128 x i8]* @mem, i32 0, i32 %s_9.4
  %temp_1.4 = bitcast i8* %temp_0.4 to i32*
  store i32 4, i32* %temp_1.4, align 4, !Stack !1
  store i32 %s_0, i32* @Global_2, align 4, !Stack !1
  ret i32 0
}